Sodium vapor lamp



Dec. 23, 1941.

-D.S.GUSWN SODIUM VAPOR LAMP Filed April 19, 1939 INVENTOR ATTORNEY Patented Dec. 23, 1941 SODIUM VAPOR LAMP Daniel S. Gustin, Bloomfield, N. 3., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, l'a., a corporation of Pennsylvania Application April 19, 1939, Serial No. 268,655

2 Claims.

. ing electrodes which are heated to an electron emitting temperature for the purpose of ionizing the gaseous atmosphere and initiating and sustaining a discharge between the electrodes. In

order to initiate the discharge so that the heat generated thereby will vaporize the metal, such as mercury or sodium which thereafter forms a constituent of the gaseous atmosphere, it has been customary to employ a rare gas, such as argon, neon, krypton, helium, or xenon, to facilitate starting.

The light emitted. by a sodium vapor lamp employing such starting gases as argon, krypton, helium, or xenon, is exceptionally low unless the pressure of such gases is also exceedingly low. Moreover, upon decrease in the gas pressure sputtering of the electrodes results which materially shortens the life of the lamp. It has been found that the efiiciency of a sodium vapor lamp can be increased by employing neon as the starting gas since the neon spectrum supplements the monochromatic spectrum of the sodium light during operation of the lamp, and furthermore thepressure of the neon can be made sumciently high that no sputtering of the electrodes results. a

Neon filled sodium vapor lamps, however, have a disadvantageous feature in that under certain conditions the red coloring of the neon is confusing. At the present time sodium vapor lamps are being employed quite extensively for airport marker lights and air-pilots have voiced considerable objection thereto since they have often mistaken the neon filled sodium vapor lamps for danger signals.

It is accordingly an object of the present invention to provide a sodium vapor lamp which will not emit any appreciable red light during or after the time it is coming up to temperature of operation.

Another object of the present invention is the provision of a sodium vapor lamp having a high efiiciency and'desirable light giving qualities by elimination of all visible traces of the customary red coloring of neon gas.

A further object of the present invention is the provision of a sodium vapor lamp utilizing a mixture of argon and neon to facilitate-starting and wherein the proportions of said mixture and its pressure is such that high efliciency is obtained without the objectionable red light characteristic of neon and sputtering of the electrodes is prevented to increase the commercial life of the lamp.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein the single figure is an elevational view of a sodium vapor lamp constructed in accordance with the present invention.

Referring now to the drawing in detail, the lamp therein shown comprises an envelope 5 having a reduced diameter portion 6 surrounding a reentrant press 7, and any suitable base 8, provided with appropriate contact terminals, is cemented or otherwise secured to the envelope. Leading-in and supporting wires are sealed into the reentrant press and two of such leading-in and support wires 9 and I 0 extend substantially the full length of the envelope and are covered by a sheathing H of insulating material, such as glass or a ceramic material capable of withstanding high temperature.

Secured to the upper extremity of the leadingin and support conductors 9 and I0 is a filamentary electrode l2 and suspended in an annular cradle 13, which is insulatingly supported by the conductors 9 and I0, is a very fragile capsule l4 containing metallic sodium which, after complete fabrication of the lamp, is dislodged from the cradle l3 and broken by striking the wall of the envelope to release the metallic sodium into the envelope.

A filamentary electrode I5, similar to the electrode I2, is supported by two remaining leadingin and support conductors l6 and I! at the opposit-e end of the envelope 5 and both of the electrodes are surrounded by an elliptical shield l8 of any suitable metal, such as nickel or the like, as is well known in the art. To initiate a local discharge and facilitate starting of the lamp, a starting electrode is is disposed adjacent the filamentary electrode l5 which is supported by a. further leading-in and supporting conductor 20.

For the purpose of deflecting the discharge during operation of the lamp, a series of spaced transversely disposed metallic baflles or deflectors 22 are cemented or otherwise secured to one of the leading-in and supporting conductors l0 and notched so that the other lead-in 9 passes therethrough. Inasmuch as the lamp attains a temperature of from 200 C. to 300 C. during operation in order to vaporize the metallic sodium, it is essential that it be protected to an appreciable extent from climatic conditions. Accordingly, the envelope 5 is positioned in a vacuum flask or the like 23 and surrounding the envelope between the reduced diameter portion 6 and the increased diameter bulbous portion is a heat insulating ring 24 which forms an end closure for the flask when the lamp is positioned therein.

To further facilitate starting of the lamp it is filled with a starting gas comprising a mixture of neon and argon. The proportion of these two gases is such that the red characteristic of neon is completely eliminated during the period the lamp is heating up to the temperature at which the sodium is vaporized and takes part in carrying the discharge, and also during the entire operation of the lamp no. red radiations are visible which might otherwise be mistaken for a danger signal. For example, an admixture of approximately 75% neon and 25% argon at a pressure of from 2 to 4 millimeters has been found very satisfactory, although other proportions may be readily used so long as the quantity of neon is small enough that no visible red radiations are observed without decreasing the pressure to the point where sputtering of the electrodes results.

The particular proportion of the admixture and its pressure of filling is also of importance inasmuch as the efficiency of such lamps is comparable or better than the eiiiciency of sodium lamps filled with neon gas only, and by the utilization of the pressure noted, sputtering of the electrodes is eliminated, thus prolonging the commercial life of the lamp.

It thus becomes obvious to those skilled in the art that a sodium vapor lamp is herein provided which emits radiations having desired characteristics by elimination of all visible traces of red so that at no time do such lamps give radiations which may be mistaken for danger signals as has been the case heretofore, particularly in the use of sodium vapor lamps for airport marker lights. Moreover, such lamps employing a mixture of neon and argon have a high efliciency and by elimination of sputtering of the electrodes, a long commercially useful life is obtained.

Although but a single embodiment of the present invention has been shown and described, it is to be noted that other modifications thereof may be made without departing mm the spirt and scope of the appended claims.

I claim:

1. A gaseous electric discharge lamp comprising an envelope, electrodes in said envelope between which a positive column discharge occurs upon the application of electrical energy thereto, and an ionizable medium in said envelope comprising sodium vapor and an admixture of approximately 75% neon and 25% argon to facilitate starting of the discharge between said electrodes and to eliminate the characteristic visible red radiation of neon, and the pressure of said admixture being approximately 2 to 4 millimeters to prevent sputtering of said electrodes and prolonging the useful life of said lamp.

2. A gaseous electric discharge lamp comprising an envelope, electrodes in said envelope between which a positive column discharge occurs upon the application of electrical energy thereto, and an ionizable medium in said envelope comprising sodium vapor and an admixture of approximately 75% neon and 25% argon to facilitate starting of the discharge between said electrodes, said admixture producing high luminous efllciency during operation of said lamp and eliminating the characteristic visible red radiation of neon, and the pressure of said admixture being approximately 2 to 4 millimeters to prevent sputtering of said electrodes and prolonging the useful life of said lamp.

DANIEL S. GUSTIN. 

